diff --git a/DECISIONS.md b/DECISIONS.md
index 63cd2da..4a407f0 100644
--- a/DECISIONS.md
+++ b/DECISIONS.md
@@ -331,3 +331,7 @@ Implementation decisions not spelled out in `memory-bank/implementation-plan.md`
 - **Points available come from sim:** `skillPointsAvailable(pilotLevel(xp), pointsSpent)`. Spending adds one level to the skill in the `skills` JSONB and one to `skill_points_spent`.
 - **Skill points can be spent any time**, including while the pilot is flying; nothing in the plan restricts it, and skills only matter when the next dispatch is checked.
 - **Check order:** pilot belongs to the player (`404 not-found`), skill exists (`404 unknown-skill`), a point is available (`409 no-skill-points`), skill below max (`409 skill-maxed`).
+
+## Step 6.13
+
+- **Acknowledging is by dispatch id and idempotent.** Ids that are unknown, belong to another player, are still in flight or were already acknowledged are skipped silently, and the response counts only those newly acknowledged. A client retry is harmless.
diff --git a/apps/server/src/game/summaries.ts b/apps/server/src/game/summaries.ts
new file mode 100644
index 0000000..57a807e
--- /dev/null
+++ b/apps/server/src/game/summaries.ts
@@ -0,0 +1,30 @@
+import type { RealTime } from "@deadhead/sim";
+import { and, eq, inArray, isNull } from "drizzle-orm";
+import type { Queryable } from "../db/client";
+import { dispatches } from "../db/schema";
+
+/**
+ * Marks "while you were away" summaries as seen (Step 6.13). Only this
+ * player's resolved, unacknowledged dispatches are touched; other ids are
+ * ignored. Returns how many were acknowledged.
+ */
+export async function acknowledgeSummaries(
+  tx: Queryable,
+  playerId: string,
+  dispatchIds: string[],
+  now: RealTime,
+): Promise<number> {
+  const updated = await tx
+    .update(dispatches)
+    .set({ acknowledgedAt: now })
+    .where(
+      and(
+        eq(dispatches.playerId, playerId),
+        inArray(dispatches.id, dispatchIds),
+        eq(dispatches.status, "resolved"),
+        isNull(dispatches.acknowledgedAt),
+      ),
+    )
+    .returning({ id: dispatches.id });
+  return updated.length;
+}
diff --git a/apps/server/src/routes/player.ts b/apps/server/src/routes/player.ts
index ade26d5..2169970 100644
--- a/apps/server/src/routes/player.ts
+++ b/apps/server/src/routes/player.ts
@@ -6,6 +6,7 @@ import { fromNodeHeaders } from "better-auth/node";
 import type { FastifyInstance } from "fastify";
 import { createPlayer } from "../game/new-player";
 import { loadPlayerState } from "../game/player-state";
+import { acknowledgeSummaries } from "../game/summaries";
 import { ApiError } from "../http/errors";
 import { registerRoute } from "../http/route";
 import type { AppContext } from "./context";
@@ -42,4 +43,10 @@ export function registerPlayerRoutes(app: FastifyInstance, ctx: AppContext): voi
   registerRoute(app, routes.getPlayerState, options, async (_input, { playerId }) =>
     withPlayer(ctx, playerId, (tx) => loadPlayerState(tx, playerId)),
   );
+
+  registerRoute(app, routes.acknowledgeSummaries, options, async (input, { playerId }) =>
+    withPlayer(ctx, playerId, async (tx, now) => ({
+      acknowledged: await acknowledgeSummaries(tx, playerId, input.dispatchIds, now),
+    })),
+  );
 }
diff --git a/apps/server/test/summaries.test.ts b/apps/server/test/summaries.test.ts
new file mode 100644
index 0000000..a6bbe53
--- /dev/null
+++ b/apps/server/test/summaries.test.ts
@@ -0,0 +1,67 @@
+import { acknowledgeSummariesResponseSchema } from "@deadhead/schema";
+import { describe, expect, it } from "vitest";
+import { makeOwner, setCredits, useTestDatabase } from "./db";
+import { call, getState, insertDispatch, signUp, useTestApp } from "./game";
+
+const database = useTestDatabase();
+const testApp = useTestApp(database);
+
+describe("acknowledging summaries", () => {
+  it("clears unacknowledged summaries while keeping the resolved effects", async () => {
+    const { app, clock } = testApp();
+    const { db } = database();
+    const guest = await signUp(app);
+    const shipId = await makeOwner(db, guest.playerId, guest.avatarId);
+    await setCredits(db, guest.playerId, 1000);
+    const record = await insertDispatch(db, {
+      playerId: guest.playerId,
+      shipId,
+      pilotId: guest.avatarId,
+      departAt: clock.now,
+    });
+    clock.now = record.arrivalAt;
+
+    const before = await getState(app, guest);
+    expect(before.summaries.map((s) => s.dispatchId)).toEqual([record.id]);
+
+    const response = await call(app, guest, "POST", "/api/summaries/acknowledge", {
+      dispatchIds: [record.id, "not-a-real-dispatch"],
+    });
+    expect(response.statusCode).toBe(200);
+    expect(acknowledgeSummariesResponseSchema.parse(response.json())).toEqual({ acknowledged: 1 });
+
+    const after = await getState(app, guest);
+    expect(after.summaries).toEqual([]);
+    expect(after.company.credits).toBe(before.company.credits);
+    expect(after.pilots[0]!.xp).toBe(before.pilots[0]!.xp);
+    expect(after.ships[0]!.locationId).toBe("moon");
+
+    // Acknowledging again changes nothing.
+    const again = await call(app, guest, "POST", "/api/summaries/acknowledge", {
+      dispatchIds: [record.id],
+    });
+    expect(again.json()).toEqual({ acknowledged: 0 });
+  });
+
+  it("does not acknowledge another player's dispatches", async () => {
+    const { app, clock } = testApp();
+    const { db } = database();
+    const owner = await signUp(app);
+    const shipId = await makeOwner(db, owner.playerId, owner.avatarId);
+    const record = await insertDispatch(db, {
+      playerId: owner.playerId,
+      shipId,
+      pilotId: owner.avatarId,
+      departAt: clock.now,
+    });
+    clock.now = record.arrivalAt;
+    await getState(app, owner);
+
+    const stranger = await signUp(app);
+    const response = await call(app, stranger, "POST", "/api/summaries/acknowledge", {
+      dispatchIds: [record.id],
+    });
+    expect(response.json()).toEqual({ acknowledged: 0 });
+    expect((await getState(app, owner)).summaries).toHaveLength(1);
+  });
+});
diff --git a/memory-bank/progress.md b/memory-bank/progress.md
index e842528..d8197e1 100644
--- a/memory-bank/progress.md
+++ b/memory-bank/progress.md
@@ -66,5 +66,5 @@
 - [x] **Step 6.10 — Contract dispatch.** `POST /api/dispatches` with `kind: "contract"` (`dispatchContract`): sim validation, fuel deducted, contract accepted, ship and pilot in flight. One integration test per sim reason (`cannot-land` via a test-only vacuum ship in mocked content), each checking nothing changed; also covers the expired-old-board case from Step 6.9.
 - [x] **Step 6.11 — Reposition dispatch.** `POST /api/dispatches` with `kind: "reposition"` (`dispatchReposition`): sim reposition validation against the player's bays, fuel only, no payout or XP; ship and pilot arrive at the destination.
 - [x] **Step 6.12 — Spend skill points.** `POST /api/pilots/:pilotId/skills` (`spendSkillPoint`): +1 skill level, +1 point spent; `409 no-skill-points`, `409 skill-maxed`, `404 unknown-skill`.
-- [ ] Step 6.13 — Acknowledge summaries
+- [x] **Step 6.13 — Acknowledge summaries.** `POST /api/summaries/acknowledge` (`src/game/summaries.ts`) sets `acknowledged_at` on the player's resolved, unacknowledged dispatches among the given ids and returns how many; resolved effects are untouched.
 - [ ] Step 6.14 — Concurrency and money safety